The present invention relates to a structure or shape of an iron core in a rotating instrument for an electric motor, an electric generator and the like. More specifically, the invention relates to a technique for a rotating instrument having high performance at a low cost, wherein, while holding high efficiency of the rotating instrument which has been made highly efficient in late years, cogging torque of a rotor in the rotating instrument is reduced to generate a stable rotating torque and improve rotating characteristics.
As is generally known, in a conventional rotating instrument, such as an electric motor and an electric generator, there has been proposed a number of techniques for improving rotating characteristics by reducing cogging torque of a rotor to generate a stable rotating torque.
More specifically, there have been attained rotating characteristics (torque characteristics) in practical use in a conventional rotating instrument by reducing the cogging torque with multiple magnetic poles in an iron core, or with different numbers of the stator poles and the rotor poles, i.e. with the stator of twelve poles and the rotor of four poles.
The rotating instruments as described above are considered to be further improved in the following points.
In detail, in the conventional rotating instrument having high efficiency, in order to improve the rotating torque characteristics by reducing the cogging torque, it has only been proposed that an electric motor or an electric generator has multiple magnetic poles in a stator or a rotor, resulting in a costly structure with an intricately wound-wire.
Also, in the conventional technique, to attain the rotating instrument having the reduced cogging torque, the pole number of the stator and the pole number of the rotor are made different. For example, the cogging torque problem has been solved by allowing the stator to have twelve poles and the rotor to have four poles. Thus, a rotating instrument having a small pole number, such as three pole stator and two pole rotor, has not been proposed due to the strong cogging torque. Also, it has been difficult in the conventional art that a rotating instrument having the stator and the rotor with the same pole number is used since such a rotating instrument generates structurally a strong caulking torque.
In view of the above, an object of the invention is to provide a rotating instrument having high efficiency and high power, wherein in the rotating instrument requiring high efficiency and high power, the cogging torque can be reduced even in a rotating instrument with the small number of poles, and even in a combination of a stator and a rotor having the same pole number, which have been difficult in the conventional art.
Further objects and advantages of the invention will be apparent from the following description of the invention.